A vessel filter is a device inserted into a blood vessel to capture particles in the blood flow. The device may be inserted into a major vein (e.g., inferior vena cava) to prevent a blood clot from reaching the lungs. Subjects that have recently suffered from trauma, or have had a heart attack (myocardial infarction), or who have experienced a major surgical procedure (e.g., surgical repair of a fractured hip, etc.) may have thrombosis in a deep vein. When the thrombus clot loosens from the site of formation and travels to the lung it can cause pulmonary embolism, which is a life-threatening condition. To prevent pulmonary embolism and other adverse conditions that may arise due to the movement of thrombus clots, a vessel filter, such as a vena cava filter, is placed into the circulatory system to intercept the thrombi and prevent them from entering the lungs. Further, it may be useful to remove or reposition implanted vessel filters.
Examples of various blood vessel filters are disclosed in U.S. Patent Application, Publication No. 2001/0000799 A1, titled “BODY VESSEL FILTER” by Wessman et al., published May 3, 2001; U.S. Patent Application, Publication No. 2002/0138097 A1, titled “ATRAUMATIC ANCHORING AND DISENGAGEMENT MECHANISM FOR PERMANENT IMPLANT DEVICE” by Ostrovsky et al., published Sep. 26, 2002; U.S. Patent Application, Publication No. 2002/0193828 A1, titled “ENDOVASCULAR FILTER” by Griffin et al., published Dec. 19, 2002; U.S. Patent Application, Publication No. 2003/0199918 A1, titled “CONVERTIBLE BLOOD CLOT FILTER” by Patel et al., published Oct. 23, 2003; U.S. Patent Application, Publication No. 2003/0208227 A1, titled “TEMPORARY VASCULAR FILTERS AND METHODS” by Thomas, published Nov. 6, 2003; U.S. Patent Application, Publication No. 2003/0208253 A1, titled “BLOOD CLOT FILTER” by Beyer et al., published Nov. 6, 2003; U.S. Pat. No. 4,425,908, titled “BLOOD CLOT FILTER” issued to Simon, dated Jan. 17, 1984; U.S. Pat. No. 4,643,184, titled “EMBOLUS TRAP” issued to Mobin-Uddin, dated Feb. 17, 1987; U.S. Pat. No. 4,817,600, titled “IMPLANT FILTER” issued to Herms et al., dated Apr. 4, 1989; U.S. Pat. No. 5,059,205, titled “PERCUTANEOUS ANTI-MIGRATION VENA CAVA FILTER” issued to El-Nounou et al., dated Oct. 22, 1991; U.S. Pat. No. 5,344,427, entitled “FILTER WITH TRIANGULAR FINGERS” issued to Cottenceau et al., dated Sep. 6, 1994; U.S. Pat. No. 5,626,605, entitled “THROMBOSIS FILTER” issued to Irie et al., dated May 6, 1007; U.S. Pat. No. 5,755,790, titled “INTRALUMINAL MEDICAL DEVICE” issued to Chevillion et al., dated May 26, 1998; U.S. Pat. No. 6,258,026 B1, titled “REMOVABLE EMBOLUS BLOOD CLOT FILTER AND FILTER DELIVERY UNIT” issued to Ravenscroft et al., dated Jul. 10, 2001; U.S. Pat. No. 6,443,972 B1, titled “VASCULAR FILTER” issued to Bosman et al., dated Sep. 3, 2002; U.S. Pat. No. 6,497,709 B1, titled “METAL MEDICAL DEVICE” issued to Heath, dated Dec. 24, 2002; U.S. Pat. No. 6,506,205 B2, titled “BLOOD CLOT FILTERING SYSTEM” issued to Goldberg et al., dated Jan. 14, 2003; and U.S. Pat. No. 6,517,559 B1, titled “BLOOD FILTER AND METHOD FOR TREATING VASCULAR DISEASE” issued to O'Connell, dated Feb. 11, 2003; U.S. Pat. No. 6,540,767 B1, titled “RECOILABLE THROMBOSIS FILTERING DEVICE AND METHOD” issued to Walak et al., dated Apr. 1, 2003, U.S. Pat. No. 6,620,183 B2, titled “THROMBOSUS FILTER WITH BREAK-AWAY ANCHOR MEMBERS” issued to DiMatteo, dated Sep. 16, 2003; each of which is incorporated herein by reference in its entirety.
Vessel filters may be permanently inserted into a blood vessel, or they may be temporarily (or removably) inserted. Removal of a vessel filter may include repositioning a vessel filter within a blood vessel after it has been inserted, or completely removing the vessel filter from the body of a subject into whom the vessel filter was inserted. A vessel filter removal or repositioning device may be used to engage and remove a vessel filter. An example of a vessel filter removal or repositioning device is found in U.S. Pat. No. 6,156,055, titled “GRIPPING DEVICE FOR IMPLANTING, REPOSITIONING, OR EXTRACTING AN OBJECT WITHIN A BODY VESSEL” issued to Ravenscroft, which is herein incorporated by reference in its entirety.
One type of vessel filter comprises a plurality of radially expandable legs that support one or more filter baskets that are conical in configuration. Such device is adapted for compression into a small size to facilitate delivery into a vascular passageway and is subsequently expanded to contact the inner wall of a body vessel. The device may be retrieved from the deployed site by compressing the radially expanded legs and the associated baskets into a compacted size for retrieval. The radially expandable legs generally also comprise engagements for anchoring the filter in position within a vessel (e.g., the vena cava). For example, the expandable legs may have hooks that can penetrate into the vessel wall and positively prevent migration of the filter in either direction along the length of the vessel. The body of such a filter is usually formed from biocompatible materials, including compressible spring metals and shape memory materials, to allow easy expansion and compression of the filter within the vessel. The hooks on the radially expandable legs may further comprise materials more elastic than the legs to permit the hooks to straighten in response to withdrawal forces and to facilitate withdrawal from the endothelium layer without risk of significant injury to the vessel wall. In one variation, the hooks are formed on the ends of a portion of the radially expandable legs, but not on others. Of course, there are many different configurations for a vessel filter, of which the above-described vessel filter is one example.
A vessel filter may be implanted in the subject's vena cava for some period (e.g., a few weeks), after which the vessel filter may be removed. During the time of implantation, the vessel filter will usually be monitored to confirm its position and condition. For example, to verify that the vessel filter has not migrated along the length of the blood vessel or become misaligned post-implantation, complex imaging systems such as MRI, CT Scan or X-ray are used to determine the condition and/or position of the vessel filter. In some versions, the implanted vessel filter contains on-board sensors or telemetry to monitor the conditions of the filter or the vessel into which the filter is implanted. In any case, monitoring may indicate when the filter may need to be removed or repositioned. The accumulation of thrombus material may result in complications that require intervention by a physician. For example, when too much thrombus material has been trapped inside and/or behind the vessel filter, the build-up may impede blood flow in the blood vessel. The pressure build-up due to the partial blockage of the blood flow may also lead to expansion of the blood vessel, which can cause tilting and/or migration of the vessel filter.
Removal or repositioning of a vessel filter may be done in a minimally invasive way, in order to reduce trauma to a subject in need of removal or repositioning of a vessel filter. For example, a vessel filter may be endoscopically removed or repositioned. However, it may be difficult to non-invasively remove a vessel filter, because it may be difficult to determine when a vessel filter is near enough to a vessel filter repositioning or removal device for the removal device to engage the vessel filter. Thus, in most instances, removal of vessel filters from a body vessel requires complex and/or expensive visualization procedures, such as MRI, X-Ray, etc.